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Solution  A homogeneous mixture of two or more substances Not just limited to liquid state Not just limited to liquid state  Solutions may or may not contain electrolytes  Electrolytes are substances that conduct electricity when dissolved

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Electrolytes and ionic compounds  All ionic compounds are electrolytes when dissolved in water  Not all ionic compounds are soluble How do we tell? How do we tell? Rules to predict solubility Rules to predict solubility  Covalent molecular compounds* are non- electrolytes – no ions produced *Except acids and bases *Except acids and bases

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Dissociation and ionization: same or different?  Ionic compounds dissociate in water Ions already exist in the solid Ions already exist in the solid  Acids or bases* ionize in water A pure acid or base contains no ions A pure acid or base contains no ions *Except strong bases like NaOH, Ca(OH) 2 are ionic *Except strong bases like NaOH, Ca(OH) 2 are ionic

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When the weak are made strong  Strong electrolytes are characterized by their nearly complete dissociation in water  Weak electrolytes dissociate to a much smaller extent.

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Recognizing acids  Mineral acids: HCl, HNO 3 etc. Conventionally H appears first in the formula Conventionally H appears first in the formula All strong acids are mineral All strong acids are mineral May be strong or weak May be strong or weak  Organic acids: CH 3 COOH etc Harder to spot Harder to spot Sometimes written with H in front – HCH 3 CO 2 Sometimes written with H in front – HCH 3 CO 2 Always weak Always weak Presence of –OH (-SH): necessary but not sufficient Presence of –OH (-SH): necessary but not sufficient Not all –OH are acidic (CH 3 OH is not an acid) Not all –OH are acidic (CH 3 OH is not an acid)

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Oxidation - reduction  Oxidation is loss of electrons  Reduction is gain of electrons Oxidation is always accompanied by reduction Oxidation is always accompanied by reduction The total number of electrons is kept constant The total number of electrons is kept constant  Oxidizing agents oxidize and are themselves reduced  Reducing agents reduce and are themselves oxidized

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Oxidation numbers  Metals are typically considered more 'cation- like' and would possess positive oxidation numbers, while nonmetals are considered more 'anion-like' and would possess negative oxidation numbers.  Oxidation number is the number of electrons gained or lost by the element in making a compound

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Predicting oxidation numbers 1.Oxidation number of atoms in element is zero 2.Oxidation number of element in monatomic ion equals charge 3.Sum of oxidation numbers in compound is zero 4.Sum of oxidation numbers in polyatomic ion equals charge F has ON –1 F has ON –1 H has ON +1; except in metal hydrides where it is –1 H has ON +1; except in metal hydrides where it is –1 Oxygen is usually –2. Exceptions: Oxygen is usually –2. Exceptions: O is –1 in hydrogen peroxide, and other peroxides O is –1 in hydrogen peroxide, and other peroxides O is –1/2 in superoxides KO 2 O is –1/2 in superoxides KO 2 In OF 2 O is +2 In OF 2 O is +2

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Position of element in periodic table determines oxidation number G1A is +1 G1A is +1 G2A is +2 G2A is +2 G3A is +3 (some rare exceptions) G3A is +3 (some rare exceptions) G5A are –3 in compounds with metals, H or with NH 4 + G5A are –3 in compounds with metals, H or with NH 4 + Exceptions are compounds with elements to right (e.g. NO 2, PF 5 ); in which case use rules 3 and 4. Exceptions are compounds with elements to right (e.g. NO 2, PF 5 ); in which case use rules 3 and 4. G6A below O (S, Se etc.) are –2 in binary compounds with metals, H or NH 4 + G6A below O (S, Se etc.) are –2 in binary compounds with metals, H or NH 4 + When combined with O or lighter halogen (e.g. SeO 2, SF 6 ) use rules 3 and 4. When combined with O or lighter halogen (e.g. SeO 2, SF 6 ) use rules 3 and 4. G7A elements are –1 in binary compounds with metals, H or NH 4 + or with a heavier halogen (e.g. Cl in BrCl 3 ) G7A elements are –1 in binary compounds with metals, H or NH 4 + or with a heavier halogen (e.g. Cl in BrCl 3 ) When combined with O or a lighter halogen, use rules 3 and 4 (e.g. Br in BrCl 3 or Cl in ClO 4 - ). When combined with O or a lighter halogen, use rules 3 and 4 (e.g. Br in BrCl 3 or Cl in ClO 4 - ).

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Identifying reagents  Those elements that tend to give up electrons (metals) are typically categorized as reducing agents and those that tend to accept electrons (nonmetals) are referred to as oxidizing agents.

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Precipitation reactions  Does one of the possible cation-anion combinations produce an insoluble salt? Initial compounds are all soluble Initial compounds are all soluble Use solubility rules to investigate Use solubility rules to investigate If yes, a precipitate is produced If yes, a precipitate is produced